Dual Mode Sensing Joystick Assembly Reducing Neutral Band
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Solution Overview
Problem
Electro-hydraulic joysticks face challenges in providing precise control and feedback due to a wide neutral band, which affects fine movements and safety, and are prone to common cause failures from redundant sensing technologies.
Innovation Solution
Implementing a dual mode sensing joystick assembly with different technologies for position and force sensing, such as magnetic and resistive systems, and a controller to synchronize start/stop points and detect errors, reducing the neutral band and enhancing safety through redundancy and plausibility checks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a wide neutral band is implemented to accommodate mechanical free-play and sensor errors, then reliability is improved, but measurement precision deteriorates
Solution Approach 1:
The control system is segmented into two independent sensing channels: a magnetic sensor for position detection and a force sensor for force detection. Each sensor type has its own signal processing path, allowing the system to accommodate mechanical free-play in the magnetic sensor while maintaining precision through force sensor feedback. This segmentation resolves the contradiction by distributing the precision requirements across different sensing modalities.
Solution Approach 2:
A force sensor acts as an intermediary element that measures the operator's input force independently of the joystick's positional displacement. This intermediary measurement allows the system to detect fine control inputs even when the magnetic position sensor exhibits drift or noise within the neutral band, thereby maintaining measurement precision while preserving the wide neutral band for reliability.
2Reliability
If redundant sensing with the same technology is implemented, then reliability is improved, but susceptibility to common cause failures worsens
Solution Approach 1:
The system changes the sensing parameter from purely positional (magnetic field displacement) to include force measurement (operator input force). By measuring force rather than position, the system achieves redundancy through a fundamentally different physical parameter that is immune to magnetic field interference, temperature drift, and mechanical free-play effects, thereby eliminating common cause failures while maintaining reliability.
3Ease of manufacture
If magnetic sensors are used for position detection, then ease of manufacture is improved, but measurement precision deteriorates due to drift and noise
Solution Approach 1:
The system replaces reliance on mechanical position sensing (magnetic displacement) with force sensing. The force sensor directly measures the operator's input force, bypassing the need for precise magnetic position detection. This substitution maintains ease of manufacture since force sensors are readily available, while dramatically improving measurement precision by eliminating magnetic field drift and noise issues.
4Reliability
If start/stop points are set far from center to compensate for errors, then reliability is improved, but ease of operation worsens due to delayed response
Solution Approach 1:
The system implements feedback using force sensor data to dynamically adjust the start/stop control points. Instead of setting fixed points far from center, the force sensor provides continuous feedback about operator input, allowing the control system to respond immediately when force is applied. This feedback mechanism maintains reliability by compensating for errors through force-based detection while improving ease of operation through immediate response.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution improves control precision, reduces production costs, and enhances safety by synchronizing start/stop points with haptic feel, minimizing common cause failures and calibration errors, and simplifying the calibration process.
Implementation Method 1
An angular position sensor system generates a first signal indicative of a travel angle of the joystick. A force sensor system generates a second signal indicative of a force applied to the joystick... using different technology for position sensing (e.g., magnetic technology)
Implementation Method 2
A large number of technologies available for sensing joystick force such as, without limitation, various strain gauge technologies (e.g., thin film, Microfused strain gauge, MEMS, peizoresistive and the like)
Data Source
AI summary
A joystick assembly includes a joystick and pre-load centering springs coupled to the joystick for biasing the joystick to a neutral position. The joystick has a central free-play zone, a transitional zone surrounding the central free-play zone in which the pre-load centering springs begin to act upon the joystick, and a load zone surrounding the transitional zone in which the pre-load centering springs exert a relatively flat spring rate upon the joystick. An angular position sensor system generates a first signal indicative of a travel angle of the joystick. A force sensor system generates a second signal indicative of a force applied to the joystick. A controller receives the first and second signals and sets start/stop points for control by the joystick approximately synchronously with the joystick moving from the transitional zone to the load zone based upon the second signal.